Previously it has been reported that chondrocytic cells produce oxygen free radicals and express the cytosolic components of NADPH oxidase. Here we report the expression of large subunit of the flavocytochrome of NADPH oxidase in chondrocytes and, further, show that the cDNA sequence contains three single base pair differences compared with the phagocyte gp91phox gene sequence. These base-pair differences may account for the different activity profiles reported between phagocytic and non-phagocytic cells.